Dec. 7, 2000 The first phase of the International Space Station (ISS), the most complex engineering project in the history of mankind, was launched some two years ago. The United States and its 15 partners have embarked on what may turn out to be the most difficult and expensive engineering project in history - building a small city in space.
Under design for 15 years, NASA's International Space Station will take at least five years and $50 billion to complete. When finished, it will cover an area nearly as large as two football fields, end-to-end.
As experimentation takes place on the ISS, one prominent goal is to develop the next generation of smart spacecraft, able to make decisions and solve problems without human intervention. Included in these experiments are several designed by Virginia Tech mechanical engineering faculty member Don Leo and graduate research assistant Mark McEver.
Leo worked as a member of an Air Force research team that tackled this problem, and he is also a member of Virginia Tech’s Center for Intelligent Material Systems and Structures. With McEver, now a doctoral candidate at Duke University, they developed specific mathematical formulas to reduce vibrations on a spacecraft and these formulas will function without programming by humans. Hence, the technology is considered "smart."
The launching of a spacecraft subjects it to vibrations. The most severe oscillations are felt at the cones at the top of the rocket. And even though they may not be catastrophic to the craft itself, these vibrations can damage the vehicle’s instrumentation during its orbit, Leo explains. This problem has plagued NASA to varying degrees during its space program.
Leo’s work on this specific concern began in 1997 when he spent a summer working on a program with the Air Force Office of Scientific Research (AFOSR). Working with Rory Ninneman, Keith Denoyer, Steve Griffin, and Dino Sciulli of Air Force Research Laboratory (AFRL), they investigated ways to reduce vibrations of space structures and noise control for payload fairings -- the shrouds on the top of the rockets that protect the payloads during the first few minutes of launch. He returned the following summer to continue working on this effort.
In 1998, the Air Force decided to enhance its research efforts in this area, putting together two teams to work on an experiment called MACE II – Middeck Active Control Experiment Reflight. MACE II is a hardware/software package that will independently learn to control vibration reduction technologies to suppress unwanted motion. If MACE II software can control deliberately induced vibrations, typical to spacecraft systems, then it will be an important contribution in the eventual design of self-reliant spacecraft able to "think" through and solve problems without human intervention, says Ninneman of the AFRL’s Space Vehicles Directorate.
"Our role," Leo says, "was to develop control algorithms that could be tested in orbit. We focused on the development of algorithms that were autonomous. No ground personnel would interact with the decision-making process once the craft left the launching pad."
The creation of MACE II follows MACE I, software that was used to test spacecraft while they were still on the ground. MACE II now eliminates the ground program, and consequently, the additional costs of testing on the ground.
Leo says that the algorithms he and McEver developed will be some of the first experiments tested on the international space station. The space station’s construction site is 250 miles above Earth, and nearly one million pounds of prefabricated building material will have to be hauled up by rockets.
Other members of the team have also developed algorithms that will be tested. The successful software will be able to adapt to changes in a structure caused by temperature fluctuations, moving parts, or the normal failures over time of mechanical subsystems. The other members include: Planning Systems, Inc., Melbourne Controls Group of Melbourne, Fl., Payload Systems of Cambridge, Mass., the University of Michigan, and Sheet Dynamics, Ltd. Of Cincinnati, Ohio.
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